Friday�s 8.9 magnitude quake unleashed a terrifying tsunami
that engulfed towns and cities on Japan�s northeastern coast, destroying
everything in its path in what Prime Minister Naoto Kan said was an
�unprecedented national disaster.�

The quake and its tectonic shift resulted from �thrust
faulting� along the boundary of the Pacific and North America plates, according
to the USGS.

The Pacific plate pushes under a far western wedge of the
North America plate at the rate of about 3.3 inches (83 millimeters) per year,
but a colossal earthquake can provide enough of a jolt to dramatically move the
plates, with catastrophic consequences.

�With an earthquake this large, you can get these huge ground
shifts,� Earle said. �On the actual fault you can get 20 meters (65 feet) of
relative movement, on the two sides of the fault.�

He said similar movements would have been seen for Chile and
Indonesia.

In December 2004, a 9.1 magnitude quake off Sumatra caused a
tsunami that killed an estimated 228,000 people. An 8.8 quake off the coast of
Chile in February 2010 killed more than 500.

There was not a similar ground shift in the 7.0 earthquake
that devastated Haiti in February 2010, Earle said.

�A magnitude 7.0 is much smaller than the earthquake that
just happened in Japan,� he said. �We�ve had aftershocks (in Japan) larger than
the Haiti earthquake.�

Kenneth Hudnut, a USGS geophysicist, said experts read data
including from global positioning systems to determine the extend of the shift.

�We know that one GPS station moved (eight feet), and we have
seen a map from GSI (Geospatial Information Authority) in Japan showing the
pattern of shift over a large area is consistent with about that much shift of
the land mass,� he told CNN. �